1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing program product, and more particularly to an image processing apparatus and an image processing program product for discriminating a dot region in an image.
2. Description of the Related Art
An image formed on a recording medium such as a sheet of paper includes a character region where characters are represented and a dot region where gray levels of a photograph, for example, are represented. When such an image formed on the recording medium is read by a scanner or any other reader to form an image on another recording medium, the read image is subjected to appropriate image processing, which differs in the character region and in the dot region. Thus, it is desirable that the dot region is discriminated from the other region in the read image with accuracy.
Japanese Laid-Open Patent Publication No. 2002-24837 describes an image processing apparatus which includes a plurality of dot detecting means each for calculating a value corresponding to the likeliness of a dot in a prescribed region in an input image with a different window size from each other, and determining means for determining whether the prescribed region is a dot region or not based on the values corresponding to the likeliness of dots calculated by the plurality of dot detecting means.
With the image processing apparatus described in Japanese Laid-Open Patent Publication No. 2002-24837, however, the determination as to whether the prescribed region is a dot region or not is made based on whether a center pixel of an isolated dot is included in the dot region or not. As such, in the case where the isolated dot has a size greater than a pixel, the region having been determined as a dot region is reduced in size by approximately half the radius of the isolated dot. As a result, there exists, in the periphery of the region having been determined as the dot region, a region that is actually included in the dot region but determined as not included in the dot region. Such an incorrectly discriminated region is excluded from a process performed on the dot region, resulting in poor image quality in the relevant region. In particular, the degraded image quality in the periphery of the dot region may lead to conspicuous degradation in quality of the image.